Charles Ellicott Commentary 2 Thessalonians 2:12

"that they all might be judged who believed not the truth, but had pleasure in unrighteousness." — 2 Thessalonians 2:12 (ASV)

That they all — This is God’s purpose in making them believe the lie: so that they all might be judged. He who desires not the death of a sinner is now said to actually lay plans with the intention of judging him—such are the bold self-contradictions of the Bible! It must not, however, be forgotten for a moment that God did not begin to will the sinner’s judgment until after He had offered him freely the love of His own blessed truth and had been rejected. Once the sinner is incurable, the only way to vindicate truth and righteousness is by hastening on his condemnation, whatever that condemnation may mean.

Who believed not the truth... — Once more, the offense for which they are condemned is insisted upon. Theirs is no fancy sin. What God wanted them to believe was not some fantastical dogma, some fiction between which and the fictions of the Man of Sin there was nothing morally to choose, but the inviolable truth by which God Himself is bound. But had pleasure in the unrighteousness (so runs the Greek): that is, they consciously gave their moral consent to the unrighteousness of 2 Thessalonians 2:10, the unrighteousness which sought to impose itself upon them, and which they would never have been led into had they loved the truth.